1. Technical Field
The present invention relates to a pattern forming method and a droplet discharge device.
2. Related Art
A multilayer substrate made of low temperature co-fired ceramics (LTCC) has excellent high-frequency characteristics and high heat resistance, and therefore is widely used for, e.g., substrates of high-frequency modules and substrates of IC packages.
Processes for manufacturing an LTCC multilayer substrate generally include a process of drawing a circuit pattern on a green sheet by using metal ink, and a process of laminating a plurality of green sheets and collectively firing the circuit pattern and each green sheet.
Regarding the process of drawing a circuit pattern, an inkjet method of discharging minute droplets of metal ink (e.g., JP-A-2006-272152, which is referred to as a “first related art example” hereinafter) is proposed to achieve high density of a circuit pattern.
The inkjet method draws a circuit pattern using a large number of droplets each ranging from several to several ten picoliters in volume, and changes the discharging position of the droplets, thereby enabling the circuit pattern to be made fine and the pitch to be made narrow.
However, when the inkjet method is used, the droplets that have landed on an object wet and spread in accordance with the state of the surface of the object.
This causes variations in size and form of the pattern after the droplets have dried.
Thus, regarding the inkjet method, a technique to suppress wetting and spreading of droplets to a desired size becomes necessary as the pattern is made finer and the pitch is made narrower.
The first related example discloses a method of applying a plurality of functional liquid materials exerting the same function (e.g., conductivity) and having different light-heat conversion efficiency onto an object one on top of the other.
Then, irradiating one functional liquid material with electromagnetic waves (e.g., laser beams) causes the functional liquid material to exert functionality, and light-heat conversion of the functional liquid material causes the other functional liquid material to exert functionality.
With this method, energy of electromagnetic waves to be input to functional liquid materials can be reduced, and a good-quality functional film pattern can be obtained.
JP-A-2006-305403, which is referred to as a “second related art example” hereinafter, discloses a method of applying electromagnetic waves (e.g., laser beams) in the normal line direction with respect to each position of the external surface of a functional liquid substance adhered onto an object.
With this method, the incident angle of electromagnetic waves to each surface of the functional liquid substance becomes small, enabling the suppression of the reflection of the electromagnetic waves to the minimum.
As a result, the applied electromagnetic waves are absorbed by the functional liquid substance with high efficiency.
If a functional liquid substance is irradiated with electromagnetic waves so that the functional liquid substance dries or dries and is fired, the functional liquid substance starts to dry on its surface.
This makes it difficult for electromagnetic wave to proceed into the interior of the functional liquid substance.
As a result, the surface of the functional liquid substance locally dries while most of its interior does not dry, and therefore the functional liquid substance wets and spreads.
In particular, if metal ink including metal fine particles is used as a functional liquid substance, most of light is absorbed into the surface of the metal ink thereby to form a metal film on the surface of the metal ink.
This metal film reflects most of the light applied to the functional liquid substance, and therefore suppresses the subsequent drying of the metal ink.
The second related art example increases the absorption coefficient of the functional liquid substance for electromagnetic waves.
On the other hand, the second related art example is not a technique of decreasing a difference in absorption coefficient between the surface and interior of the functional liquid substance.
Therefore, the second related art example cannot achieve sufficiently uniform dry state of the functional liquid substance.